You are right there should have been multiple notifications but then again sometimes it just seems to slip between the cracks.
I used to know a lawyer who regularly bought up tax sale property. He didn’t do it on the sly tho. What he would do is buy the owner’s right of redemption from him.
One time he asked the owner if he was willing to sell his right and the guy had no idea his property was being sold for taxes. The guy went down and paid them immediately.
I live on Long Island and I know the towns are diligent in sending out several notices before beginning any proceedings.